Quadrature magnetic resonance imaging coils, and more recently, multicoil systems using a plurality of independent data acquisition channels, are generally known in the art. Quadrature magnetic resonance systems offer advantages over previous magnetic resonance imaging techniques in that they provide a better signal to noise ratio by using both component vectors of the circularly polarized field of the magnetic resonance phenomenon, and lower RF transmitter power requirements when used as transmit coils. Multicoil systems offer some or all of the above-noted advantages, plus additional advantages in enhancing the imaging signal to noise ratio due to the reduced imaging volume of each independent coil and data acquisition path in the multicoil system. However, when these systems are used for magnetic resonance imaging, the isolation of the signal currents in one coil mode or coil system from currents in the other mode or coil system must be at a high level to obtain the benefits of quadrature operation, or multicoil operation.
Those skilled in the art will appreciate that it is desirable to reduce or eliminate the inductive coupling between the two coil systems forming the RF quadrature coil used in a magnetic resonance imaging system in order to solve these and other problems. Additionally, it is desirable to reduce or eliminate the inductive coupling between the various coil systems in a multicoil configuration. Ideally there should be no inductive coupling between the coil systems comprising the RF quadrature coil or multicoil system. Previously the adjustment of such coils to minimize the coupling between the coils was accomplished by either the physical movement of the coils or the physical adjustment of a variable element to electrically accomplish the same result.
Changing a single element generally alters the tuning or other coil parameters. In the past, adjusting the isolation or orthogonality of a coil has yielded undesirable manual secondary adjustment of one or more other coil parameters. Further, if physical adjustment of the location of the coils is employed to accomplish this result, many coil formations are eliminated as a practical matter, thereby dramatically decreasing the versatility of these systems.
Providing optimum orthogonality adjustment is required to improve the signal to noise ratio of MRI and MRS signals. Furthermore, such an adjustment is essential in order to implement more flexible, and anatomically conformal MR coils operating in quadrature and/or multi-coil modes. Also, flexible surface coils impart advantages in filling factor and patient comfort; however, the variability of the coil geometry generally precludes the use of the quadrature technique due to the loss of defined geometry. Thus a need exists for a mechanism to provide optimal tuning and orthogonality adjustment to improve the signal to noise ratio of MRI and or MRS signals for flexible and variable quadrature coil configurations.